Post doped nitrogen-decorated hollow carbon spheres as a support for Co Fischer-Tropsch catalysts

Abstract

In this study the outer surface of porous hollow carbon spheres (HCSs) materials were functionalized by N-doping using a post-synthesis method and they were used as a Fischer-Tropsch catalyst support. Melamine was used as the nitrogen source, and carbonization was performed at different temperatures (600 and 900 °C) to introduce variable levels of N into the HCSs, with different bonding configurations. This procedure allowed for the incorporation of up to 13% N. Our results show that post-synthesis N-doping introduced marginal defects into the carbon framework and this did not affect the thermal stability of the materials. XPS studies revealed that the surface content on these materials varied and provided evidence for temperature-tunable bonding configurations. Effects associated with post-synthesis N-doping were apparent on the Co catalyst (˜10 wt.%) properties such as the inhibited reduction caused by a metal-support interaction observed by the H2-TPR and in situ PXRD techniques. As a consequence the Fischer-Tropsch performance was influenced as both the activity and stability were improved on the catalysts supported on the N-doped materials. TEM analysis of the spent catalysts demonstrated the influence of N-doping on the sintering characteristics of Co, with particles > 30 nm measured on the N-free catalyst while N-doped samples had sizes < 15 nm.